As shown in Laid-open Japanese Utility Model Applications No. S53-3395 and S53-4521, seat suspension structures for two-wheeled vehicles or the like are conventionally known, which use a seat damper interposed between a one-seater seat for the driver to sit on and the vehicle body to provide a cushion, so as to absorb shock and vibration transmitted to the driver from the vehicle body via the seat. The seat is mounted to the vehicle body such as to be fixed at the front end with a hinge mechanism while allowing its rear side to deflect in the up and down direction. The seat includes a U-shaped seat bracket, which is a mounting part for securing a seat damper to the backside of the seat. A mounting part formed by a pair of mounting pieces is provided on the vehicle body to attach the seat damper. The seat bracket and the mounting part of the vehicle body are arranged such that they are located on the same plane. The seat damper includes a tubular member, a rod coaxially provided to the tubular member to slide axially on the inner circumferential surface of the tubular member, and a compression spring. The compression spring is set to surround the rod and the tubular member and seated on the respective bearing plates on the outer circumferences of the tubular member and the rod. Mounting holes extending through the tubular member and the rod perpendicularly to their axes are formed in portions closer to ends than the respective bearing plates of the tubular member and the rod, and pins are inserted into the respective mounting holes as well as the seat bracket and the mounting part on the vehicle body side. The seat damper is thereby attached to the respective mounting parts of the seat bracket and the vehicle body to be rotatable with the strokes of the seat damper when the seat moves up and down. The seat is formed by covering a frame, which includes the seat mounting pieces and is provided with a foam material or the like, with skin or leather.
With the seat suspension structure shown in Japanese Utility Model Application Laid-open No. S53-3395 and S53-4521, however, the seat bracket for attaching the seat damper and the mounting part of the vehicle body need to be positioned accurately on the same plane. Since the distal end of the seat is fixed with a hinge mechanism while the rear end is rotatable up and down, the seat damper needs to be attached with pins as mentioned above so that it is rotatable relative to the seat bracket and the mounting part of the vehicle body to perform the stroke motion. That is, since the seat damper is coupled by inserting pins between itself and the seat bracket or the mounting part of the vehicle body, if the seat bracket and the mounting part of the vehicle body are not on the same plane, even if the pin may be inserted into one of the seat bracket and the mounting part of the vehicle body, it can not be inserted to the other. Even if the precision error is within a range that still allows forcible mounting, a force caused by such forcible mounting will act on the seat damper and may inhibit smooth stroke motion thereof, or may act laterally on the seat relative to the vehicle body at every stroke, which may inhibit the driver's control of the vehicle. Consequently the positioning of the seat bracket and the mounting part of the vehicle body for attaching the seat damper requires high accuracy and is an impediment to an improvement in production efficiency in the process step of attaching the seat damper. Also, the seat bracket and the mounting part of the vehicle body require sufficient rigidity in view of the need to keep the seat damper fixedly in position so that the stroke motion of the seat damper will be in a constant direction.